2007 Porsche Cayman S – Tour of Engine Sensors and Components

Posted by newhillgarage ⋅ December 1, 2023

As discussed in other articles, starting here, I have been rebuilding the M97 engine of my 2007 Cayman S. One reliablity upgrade that I did was to purchase a new engine wiring harness from Porsche. I did this for several reasons. It is a 5 owner car with little maintenance history. I can see that the harness has been hacked. Also, I feel that there is a point, which I cannot objectively identify, where wiring harnesses start to age out. It can be subtle. Increased resistances on the wiring path to sensors can cause the expected range of sensor values to shift subtlely. Remember, this is an analog car. Very generally speaking, sensors take a nominal 12volt system operating voltage, carve out a range from 2V to 10V, and make ECU decisions based on the percentage voltage returned in that range. Add in a few ohms of wire resistance and the values are no longer representative of what is actually happening. Catostrophic? No. Annoying? Certainly. Anyway, as I was laying in my new wiring harness, I realized that this was a good opportunity to shoot some video to talk about the locations of sensor and components on the engine. And also talk about the types of terminal end clips that are used. Trust me, it was frustrating as I removed the engine to determine just how I should approach each clip to get it to release. I must admit that I broke a few, just not really understanding how they worked. If nothing else, this video will give you an idea regarding how each clip is designed with regard to releasing it from its sensor or component.

Here is a photo of my new wiring harness.

So, since a picture is worth a thousand words, and a video consists of thousands of pictures, below are the links to a part 1 and part 2 video I did on sensors and components. If you come across this post looking to identify a specific item, note that I have added subtitles that you can view as you fast forward through the videos. Spoiler alert. The crankshaft sensor wound up at the very end of the second video. I probably should have done it first!

NOTE: At 3:20 in the following video, I discuss the location of the solenoids for Variocam and Variocam +. I have discovered that I stated it backwards! The solenoid for the Variocam (inlet valve active advance mechanism) is on the left in the video. Easiest to remember is that it is the one closest to the end of the cylinder head.

I don’t think I mentioned it in the video but there is a small in-line valve that is a switch to bring in the fuel vapor from the carbon canister and inject it into the inlet manifold immediately downstream of the throttle valve. It is hard to see but it is immediately behind the #5 intake runner. Its harness connection is the wire clip type.

As a bonus, I’m going to do a quick tutorial on the “resonance flap valves”. Probably most of us don’t even know that they exist, as they are hidden. Very basically, there are flap valves in the intake plenum, very similar to throttle valves, that serve to close off the two halves of the engine, such that it “breathes” like two independent 3 cylinder engines. Although this is just an educated guess, Porsche closes the flaps during low rpm/low load conditions, in order to improve emissions performance. Of course, the real fun starts when the flaps are open, allowing optomized cylinder filling during high speed operation. This is a complex subject but very generally, pressure pulses are generated every time an intake valve closes. These pulses bounce around the plenum. When strategically designed, a pulse can arrive at another intake valve just as it is opening, serving to ram extra intake air/fuel mixture into that cylinder. BTW, headers with equal length tubes do the same on the exhaust side of things. The resonance flap valves are activated by vacuum driven “change over” valves, which are controlled by the ECU. Here are a few pictures.

Left and right intake manifolds. The short piece in the bottom of the photo has a flap valve and is “downstream” of the throttle valve. The short piece in the top has a flap valve.

Each of the two entry paths into the manifold can feed air to all 3 cylinders.

The flap valve just downstream of the throttle valve. When closed, the air is split into equal parts.

The flap valve in the other short connecting piece.

Everything assembled. You’d never know these were there!

The changeover valves (one on each side) are located between the runners on the inlet plenum.

Anyway, I hope this will help you out when you think you need to locate a sensor or component for replacement. Of course, everything is harder to see looking down into the engine in its compartment but if you know what you are looking for, that certainly helps!

The next article in this series is Engine Re-Assembly Part 2.

Bonus content- Here is a short animation that shows how lifters work. I always thought of them as “pumping up” but yes, there is also a “pumping down” action.